Clinical Effect And Quality Of Vision Early Post SBK

Objective： To evaluate the efficacy and safety of SBK for thecorrection of moderate and high myopia with visual acuity, refraction andanterior segment measurements performed by Sirius. To assess the quality ofvision early post SBK with corneal and total optical wavefront aberration,photopic and mesopic contrast sensitivity.Methods：(1) Sixty eight myopic eyes of35consecutive patientswere included in the study. To assess the repeatability of central cornealthickness (CCT) performed by a Scheimpflug camera combined withPlacido corneal topography (Sirius) in pre and post refractive eyes.Tocompare the agreement and differentiation of the Sirius with ultrasoundpachymetry in the measurement of CCT.(2) All patients were evaluatedtwo weeks, one month, three months postoperatively. The main anteriorsegment measurements included CCT, anterior and posterior cornealtangential curvature, anterior chamber depth (ACD) and volume (ACV).Using the anterior segment measurements, visual acuity and refraction toevaluate the efficacy and safety of SBK for the correction of moderate andhigh myopia.(3) To assess the quality of vision early post SBK with corneal and total optical wavefront aberration, photopic and mesopiccontrast sensitivity.Results：1. The ICC of the Sirius were0.988(pre-op),0.993(2w),0.992(1mo),0.996(3mo), respectively.2. The95%limits of agreement in CCT were-14.04to11.20μm(pre-op),-21.10to5.16μm (2w),-28.00to10.76μm (1mo),-27.18to12.30μm (3mo), respectively. The difference value of Sirius andultrasound pachymetry was-1.42±6.44μm (pre-op),-8.62±9.89μm(post-op).The postoperative Sirius measurements were significantly thinnerthan ultrasound pachymetry measurements (P<0.05).3. The CCT values of the Sirius and ultrasound pachymetry werepositively related by linear correlation analysis, r=0.970(pre-op),0.987(2w),0.980(1mo),0.978(3mo).4. The preoperative UCVA was0.06±0.04, BCVA was0.97±0.13, thepostoperative UCVA was1.13±0.24at2weeks,1.15±0.28at1month,1.18±0.27at3months. Three months after surgery UCVA of43/43eyes reached or exceeded their preoperative BCVA. Postoperative manifestspherical equivalent (MSE) was0.91±0.61D at2weeks,0.77±0.38D at1month,0.65±0.44D at3months. The refraction was converting toemmetropic from hypermetropic postoperatively.5. The preoperative IOP measurement was12.95±2.12mmHg, The postoperative IOP measurement was9.61±1.18~9.72±1.05mmHg whichwas lower than the preoperative measurement. But there was no significantdifference between the preoperative(13.52±1.99mmHg) andpostoperative(13.52±1.29~13.76±1.10mmHg) corrected IOP (P>0.05).6. The CCT values at3months was7.44μm thicker than themeasurement at2weeks (P=0.000), and5.70μm thicker than themeasurement at1month (P=0.000). The anterior corneal tangentialcurvature in central3mm region at3months was0.29D higher than that at2weeks(P<0.05), and0.03D higher than that at1month(P>0.05). Theincrassation of CCT agreed with the incrassation of anterior cornealtangential curvature in central3mm region.7. There was no significant difference between the preoperative andpostoperative posterior corneal tangential curvature (P>0.05).8. The ACD values decreased60~70μm early post SBK (P=0.000),but it returned to preoperative levels at3months after surgery. There wasno significant difference between the preoperative and postoperative ACV(P>0.05).9. There was no significant difference between the preoperative andpostoperative anterior corneal total aberration(P>0.05).Compared withpreoperation, corneal high order aberrations increased by3times, sphericalaberration, coma aberration, trefoil aberration, quadrifoil aberration allincreased significantly. Spherical aberration became the main postoperative corneal high order aberrations. There was postive correlation between theabsolute value of sphere and postoperative corneal spherical aberrationincrement(r=0.83,P=0.000).10. The total optical aberrations decreased significantly after SBK(P=0.000). Compared with preoperation, total high order aberrationsincreased by1.5times, coma and spherical aberration increasedsignificantly. Coma aberration became the main postoperative total highorder aberrations. There was postive correlation between the absolute valueof sphere and postoperative coma aberration increment(r=0.32,P=0.047).11. Although photopic and mesopic contrast sensitivity fluctuatedmildly after SBK, the measurements did not decrease significantly.Compared with preoperation, mesopic contrast sensitivity at3monthsincreased0.294and0.296at12and18c/d respectively.Conclusion:1. The measurements of CCT with Sirius yielded excellentrepeatability.There was great agreement and positive correlation betweenSirius and ultrasound pachymetry. These indicated that the measurementsof Sirius were accurately.2. All patients’ postoperative UCVA reached or exceeded theirpreoperative BCVA. There was no significant difference between thepreoperative and postoperative ACV and corrected IOP. As the CCTincreased gradually, the refraction was converting to emmetropic from hypermetropic. Posterior corneal surface remained stable after SBK. Fromthis research we considered that SBK for the correction of moderate andhigh myopia was safe and effective.3. There was no significant difference between the preoperative andpostoperative anterior corneal total aberration.Compared with preoperation,corneal high order aberrations increased by3times. Spherical aberrationbecame the main postoperative corneal high order aberrations. There waspostive correlation between the absolute value of sphere and postoperativecorneal spherical aberration increment.The total optical aberrationsdecreased significantly after SBK. Compared with preoperation, total highorder aberrations increased by1.5times, coma and spherical aberrationincreased significantly. Coma aberration became the main postoperativetotal high order aberrations. It indicated that spherical aberration waspartial compensated by the internal aberrations of the eye.Although thecorneal and ocular aberrations increased after SBK, photopic and mesopiccontrast sensitivity fluctuated did not decrease significantly. Comparedwith preoperation, mesopic contrast sensitivity at3months increased0.294and0.296at12and18c/d respectively. So we considered that the patientshad a good quality of vision early post SBK.